Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.42	5.576%	$31.0605	$31.06	$31.05	$31.10
Purchase #2	$123.56	6.301%	$131.3455	$131.35	$131.35	$131.30
Purchase #3	$159.71	9.636%	$175.0997	$175.10	$175.10	$175.10
Purchase #4	$119.25	3.872%	$123.8674	$123.87	$123.85	$123.90
Purchase #5	$117.31	4.678%	$122.7978	$122.80	$122.80	$122.80
Purchase #6	$168.39	8.443%	$182.6072	$182.61	$182.60	$182.60
Purchase #7	$247.87	9.345%	$271.0335	$271.03	$271.05	$271.00
7 purchase totals =	$965.51		$1,037.8116	$1,037.82	$1,037.80	$1,037.80